Not applicable.
1. Field of the Invention
The present invention relates to the blending of polymeric materials and fillers to form free flowing particles.
2. Description of the Related Art
U.S. Pat. No. 5,552,457 is directed to a process for making resin-composite particulates of syndiotactic-1,2-polybutadiene and carbon black without using a conventional mixer. The carbon black and resin are mixed in an aqueous medium at an elevated temperature above the melting point or softening point of the resin, the medium is cooled and the masterbatch powder is recovered.
U.S. Pat. No. 3,920,604 is directed to a process for producing pourable, filler-containing polymer particles in which the polymer is dissolved in a volatile organic solvent, carbon black is added to the dissolved polymer, and the solvent is flash evaporated.
U.S. Pat. No. 4,994,534 is directed to the formation of sticky polymers in which the polymerization is said to take place at a temperature in excess of the softening temperature of the polymer, and in the presence of a particulate material having a mean particle size of from about 0.01 to about 10 micron meters.
In one aspect, the present invention relates to a method for the formation of a free flowing polymer/filler masterbatch powder, which method comprises intimately mixing a polymer and a filler for a time and under shear conditions sufficient to convert the components into a free flowing associated composition of polymer and filler.
In another aspect, the present invention relates to the product of the method set forth above.
In yet another aspect, the present invention relates to a molded or extruded article made from the product set forth above.
The present invention provides a means for forming a free flowing blend of a polymeric material and a filler. Suitable polymeric materials include both natural rubber and synthetic rubbers. Synthetic rubbers include, but are not limited to, for example, ethylene/alpha-olefin/non-conjugated polyene (EPDM) rubbers, ethylene/alpha-olefin (EPR) rubbers, styrene/butadiene rubbers, acrylonitrile/butadiene (NBR) rubbers, polychloroprene rubbers, polybutadiene rubbers, isobutylene-isoprene copolymers, etc. The polymeric component also includes mixtures of two or more different polymeric materials. In a preferred embodiment, the polymeric material, prior to blending, is substantially or completely free of filler material.
Suitable fillers include any filler conventionally used in polymer compounding, including carbon black, hydrated amorphous silica, diatomaceous earth, talc, calcium carbonate, etc., and may include mixtures of two or more different fillers.
The powders according to the present invention may have a weight ratio of polymer to filler from about 1:0.15 to about 1:10, preferably from about 1:0.15 to about 1:1.5, depending on the constituent materials and the application therefor.
The polymer/filler powders of the present invention may be processed by well known means into, e.g., various types of end product molded or extruded articles, including tires, hoses, roof sheeting, weatherstripping, belts, wire and cable covers, etc., and may contain other conventional additives such as processing aids, antioxidants, antiozonants, etc.
The powders of the present invention may be formed by subjecting the desired amounts of polymer and filler, preferably in a substantially dry state, to shear conditions in an internal mixer such as Brabenders, continuous screw extruders, Banburys, etc. and for a time sufficient to form the powder. For present purposes, a dry state is defined as free from polymerization medium solvents and/or water. In a preferred embodiment, the polymer and filler are blended in a mixer, preferably for about 1 to about 5 minutes. As will be demonstrated more fully below, the quality of the powder may be controlled by varying a number of parameters, including the volume loading of the mixer, mixing temperature, mixing time, mixing shear stress, and the blend ratio of the polymer and filler. In certain embodiments, the filler and/or polymer may additionally comprise an extender oil.